xref: /netbsd/sys/kern/uipc_mbuf.c (revision f677aab4)

/*	$NetBSD: uipc_mbuf.c,v 1.251 2023/04/12 06:48:08 riastradh Exp $	*/

/*
 * Copyright (c) 1999, 2001, 2018 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
 * NASA Ames Research Center, and Maxime Villard.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Copyright (c) 1982, 1986, 1988, 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)uipc_mbuf.c	8.4 (Berkeley) 2/14/95
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: uipc_mbuf.c,v 1.251 2023/04/12 06:48:08 riastradh Exp $");

#ifdef _KERNEL_OPT
#include "opt_mbuftrace.h"
#include "opt_nmbclusters.h"
#include "opt_ddb.h"
#include "ether.h"
#endif

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/atomic.h>
#include <sys/cpu.h>
#include <sys/proc.h>
#include <sys/mbuf.h>
#include <sys/kernel.h>
#include <sys/syslog.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/percpu.h>
#include <sys/pool.h>
#include <sys/socket.h>
#include <sys/sysctl.h>

#include <net/if.h>

pool_cache_t mb_cache;	/* mbuf cache */
static pool_cache_t mcl_cache;	/* mbuf cluster cache */

struct mbstat mbstat;
int max_linkhdr;
int max_protohdr;
int max_hdr;
int max_datalen;

static void mb_drain(void *, int);
static int mb_ctor(void *, void *, int);

static void sysctl_kern_mbuf_setup(void);

static struct sysctllog *mbuf_sysctllog;

static struct mbuf *m_copy_internal(struct mbuf *, int, int, int, bool);
static struct mbuf *m_split_internal(struct mbuf *, int, int, bool);
static int m_copyback_internal(struct mbuf **, int, int, const void *,
    int, int);

/* Flags for m_copyback_internal. */
#define	CB_COPYBACK	0x0001	/* copyback from cp */
#define	CB_PRESERVE	0x0002	/* preserve original data */
#define	CB_COW		0x0004	/* do copy-on-write */
#define	CB_EXTEND	0x0008	/* extend chain */

static const char mclpool_warnmsg[] =
    "WARNING: mclpool limit reached; increase kern.mbuf.nmbclusters";

MALLOC_DEFINE(M_MBUF, "mbuf", "mbuf");

static percpu_t *mbstat_percpu;

#ifdef MBUFTRACE
struct mownerhead mowners = LIST_HEAD_INITIALIZER(mowners);
struct mowner unknown_mowners[] = {
	MOWNER_INIT("unknown", "free"),
	MOWNER_INIT("unknown", "data"),
	MOWNER_INIT("unknown", "header"),
	MOWNER_INIT("unknown", "soname"),
	MOWNER_INIT("unknown", "soopts"),
	MOWNER_INIT("unknown", "ftable"),
	MOWNER_INIT("unknown", "control"),
	MOWNER_INIT("unknown", "oobdata"),
};
struct mowner revoked_mowner = MOWNER_INIT("revoked", "");
#endif

#define	MEXT_ISEMBEDDED(m) ((m)->m_ext_ref == (m))

#define	MCLADDREFERENCE(o, n)						\
do {									\
	KASSERT(((o)->m_flags & M_EXT) != 0);				\
	KASSERT(((n)->m_flags & M_EXT) == 0);				\
	KASSERT((o)->m_ext.ext_refcnt >= 1);				\
	(n)->m_flags |= ((o)->m_flags & M_EXTCOPYFLAGS);		\
	atomic_inc_uint(&(o)->m_ext.ext_refcnt);			\
	(n)->m_ext_ref = (o)->m_ext_ref;				\
	mowner_ref((n), (n)->m_flags);					\
} while (/* CONSTCOND */ 0)

static int
nmbclusters_limit(void)
{
#if defined(PMAP_MAP_POOLPAGE)
	/* direct mapping, doesn't use space in kmem_arena */
	vsize_t max_size = physmem / 4;
#else
	vsize_t max_size = MIN(physmem / 4, nkmempages / 4);
#endif

	max_size = max_size * PAGE_SIZE / MCLBYTES;
#ifdef NMBCLUSTERS_MAX
	max_size = MIN(max_size, NMBCLUSTERS_MAX);
#endif

	return max_size;
}

/*
 * Initialize the mbuf allocator.
 */
void
mbinit(void)
{

	CTASSERT(sizeof(struct _m_ext) <= MHLEN);
	CTASSERT(sizeof(struct mbuf) == MSIZE);

	sysctl_kern_mbuf_setup();

	mb_cache = pool_cache_init(msize, 0, 0, 0, "mbpl",
	    NULL, IPL_VM, mb_ctor, NULL, NULL);
	KASSERT(mb_cache != NULL);

	mcl_cache = pool_cache_init(mclbytes, COHERENCY_UNIT, 0, 0, "mclpl",
	    NULL, IPL_VM, NULL, NULL, NULL);
	KASSERT(mcl_cache != NULL);

	pool_cache_set_drain_hook(mb_cache, mb_drain, NULL);
	pool_cache_set_drain_hook(mcl_cache, mb_drain, NULL);

	/*
	 * Set an arbitrary default limit on the number of mbuf clusters.
	 */
#ifdef NMBCLUSTERS
	nmbclusters = MIN(NMBCLUSTERS, nmbclusters_limit());
#else
	nmbclusters = MAX(1024,
	    (vsize_t)physmem * PAGE_SIZE / MCLBYTES / 16);
	nmbclusters = MIN(nmbclusters, nmbclusters_limit());
#endif

	/*
	 * Set the hard limit on the mclpool to the number of
	 * mbuf clusters the kernel is to support.  Log the limit
	 * reached message max once a minute.
	 */
	pool_cache_sethardlimit(mcl_cache, nmbclusters, mclpool_warnmsg, 60);

	mbstat_percpu = percpu_alloc(sizeof(struct mbstat_cpu));

	/*
	 * Set a low water mark for both mbufs and clusters.  This should
	 * help ensure that they can be allocated in a memory starvation
	 * situation.  This is important for e.g. diskless systems which
	 * must allocate mbufs in order for the pagedaemon to clean pages.
	 */
	pool_cache_setlowat(mb_cache, mblowat);
	pool_cache_setlowat(mcl_cache, mcllowat);

#ifdef MBUFTRACE
	{
		/*
		 * Attach the unknown mowners.
		 */
		int i;
		MOWNER_ATTACH(&revoked_mowner);
		for (i = sizeof(unknown_mowners)/sizeof(unknown_mowners[0]);
		     i-- > 0; )
			MOWNER_ATTACH(&unknown_mowners[i]);
	}
#endif
}

static void
mb_drain(void *arg, int flags)
{
	struct domain *dp;
	const struct protosw *pr;
	struct ifnet *ifp;
	int s;

	KERNEL_LOCK(1, NULL);
	s = splvm();
	DOMAIN_FOREACH(dp) {
		for (pr = dp->dom_protosw;
		     pr < dp->dom_protoswNPROTOSW; pr++)
			if (pr->pr_drain)
				(*pr->pr_drain)();
	}
	/* XXX we cannot use psref in H/W interrupt */
	if (!cpu_intr_p()) {
		int bound = curlwp_bind();
		IFNET_READER_FOREACH(ifp) {
			struct psref psref;

			if_acquire(ifp, &psref);

			if (ifp->if_drain)
				(*ifp->if_drain)(ifp);

			if_release(ifp, &psref);
		}
		curlwp_bindx(bound);
	}
	splx(s);
	mbstat.m_drain++;
	KERNEL_UNLOCK_ONE(NULL);
}

/*
 * sysctl helper routine for the kern.mbuf subtree.
 * nmbclusters, mblowat and mcllowat need range
 * checking and pool tweaking after being reset.
 */
static int
sysctl_kern_mbuf(SYSCTLFN_ARGS)
{
	int error, newval;
	struct sysctlnode node;

	node = *rnode;
	node.sysctl_data = &newval;
	switch (rnode->sysctl_num) {
	case MBUF_NMBCLUSTERS:
	case MBUF_MBLOWAT:
	case MBUF_MCLLOWAT:
		newval = *(int*)rnode->sysctl_data;
		break;
	case MBUF_NMBCLUSTERS_LIMIT:
		newval = nmbclusters_limit();
		break;
	default:
		return EOPNOTSUPP;
	}

	error = sysctl_lookup(SYSCTLFN_CALL(&node));
	if (error || newp == NULL)
		return error;
	if (newval < 0)
		return EINVAL;

	switch (node.sysctl_num) {
	case MBUF_NMBCLUSTERS:
		if (newval < nmbclusters)
			return EINVAL;
		if (newval > nmbclusters_limit())
			return EINVAL;
		nmbclusters = newval;
		pool_cache_sethardlimit(mcl_cache, nmbclusters,
		    mclpool_warnmsg, 60);
		break;
	case MBUF_MBLOWAT:
		mblowat = newval;
		pool_cache_setlowat(mb_cache, mblowat);
		break;
	case MBUF_MCLLOWAT:
		mcllowat = newval;
		pool_cache_setlowat(mcl_cache, mcllowat);
		break;
	}

	return 0;
}

#ifdef MBUFTRACE
static void
mowner_convert_to_user_cb(void *v1, void *v2, struct cpu_info *ci)
{
	struct mowner_counter *mc = v1;
	struct mowner_user *mo_user = v2;
	int i;

	for (i = 0; i < MOWNER_COUNTER_NCOUNTERS; i++) {
		mo_user->mo_counter[i] += mc->mc_counter[i];
	}
}

static void
mowner_convert_to_user(struct mowner *mo, struct mowner_user *mo_user)
{

	memset(mo_user, 0, sizeof(*mo_user));
	CTASSERT(sizeof(mo_user->mo_name) == sizeof(mo->mo_name));
	CTASSERT(sizeof(mo_user->mo_descr) == sizeof(mo->mo_descr));
	memcpy(mo_user->mo_name, mo->mo_name, sizeof(mo->mo_name));
	memcpy(mo_user->mo_descr, mo->mo_descr, sizeof(mo->mo_descr));
	percpu_foreach(mo->mo_counters, mowner_convert_to_user_cb, mo_user);
}

static int
sysctl_kern_mbuf_mowners(SYSCTLFN_ARGS)
{
	struct mowner *mo;
	size_t len = 0;
	int error = 0;

	if (namelen != 0)
		return EINVAL;
	if (newp != NULL)
		return EPERM;

	LIST_FOREACH(mo, &mowners, mo_link) {
		struct mowner_user mo_user;

		mowner_convert_to_user(mo, &mo_user);

		if (oldp != NULL) {
			if (*oldlenp - len < sizeof(mo_user)) {
				error = ENOMEM;
				break;
			}
			error = copyout(&mo_user, (char *)oldp + len,
			    sizeof(mo_user));
			if (error)
				break;
		}
		len += sizeof(mo_user);
	}

	if (error == 0)
		*oldlenp = len;

	return error;
}
#endif /* MBUFTRACE */

void
mbstat_type_add(int type, int diff)
{
	struct mbstat_cpu *mb;
	int s;

	s = splvm();
	mb = percpu_getref(mbstat_percpu);
	mb->m_mtypes[type] += diff;
	percpu_putref(mbstat_percpu);
	splx(s);
}

static void
mbstat_convert_to_user_cb(void *v1, void *v2, struct cpu_info *ci)
{
	struct mbstat_cpu *mbsc = v1;
	struct mbstat *mbs = v2;
	int i;

	for (i = 0; i < __arraycount(mbs->m_mtypes); i++) {
		mbs->m_mtypes[i] += mbsc->m_mtypes[i];
	}
}

static void
mbstat_convert_to_user(struct mbstat *mbs)
{

	memset(mbs, 0, sizeof(*mbs));
	mbs->m_drain = mbstat.m_drain;
	percpu_foreach(mbstat_percpu, mbstat_convert_to_user_cb, mbs);
}

static int
sysctl_kern_mbuf_stats(SYSCTLFN_ARGS)
{
	struct sysctlnode node;
	struct mbstat mbs;

	mbstat_convert_to_user(&mbs);
	node = *rnode;
	node.sysctl_data = &mbs;
	node.sysctl_size = sizeof(mbs);
	return sysctl_lookup(SYSCTLFN_CALL(&node));
}

static void
sysctl_kern_mbuf_setup(void)
{

	KASSERT(mbuf_sysctllog == NULL);
	sysctl_createv(&mbuf_sysctllog, 0, NULL, NULL,
		       CTLFLAG_PERMANENT,
		       CTLTYPE_NODE, "mbuf",
		       SYSCTL_DESCR("mbuf control variables"),
		       NULL, 0, NULL, 0,
		       CTL_KERN, KERN_MBUF, CTL_EOL);

	sysctl_createv(&mbuf_sysctllog, 0, NULL, NULL,
		       CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
		       CTLTYPE_INT, "msize",
		       SYSCTL_DESCR("mbuf base size"),
		       NULL, msize, NULL, 0,
		       CTL_KERN, KERN_MBUF, MBUF_MSIZE, CTL_EOL);
	sysctl_createv(&mbuf_sysctllog, 0, NULL, NULL,
		       CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
		       CTLTYPE_INT, "mclbytes",
		       SYSCTL_DESCR("mbuf cluster size"),
		       NULL, mclbytes, NULL, 0,
		       CTL_KERN, KERN_MBUF, MBUF_MCLBYTES, CTL_EOL);
	sysctl_createv(&mbuf_sysctllog, 0, NULL, NULL,
		       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
		       CTLTYPE_INT, "nmbclusters",
		       SYSCTL_DESCR("Limit on the number of mbuf clusters"),
		       sysctl_kern_mbuf, 0, &nmbclusters, 0,
		       CTL_KERN, KERN_MBUF, MBUF_NMBCLUSTERS, CTL_EOL);
	sysctl_createv(&mbuf_sysctllog, 0, NULL, NULL,
		       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
		       CTLTYPE_INT, "mblowat",
		       SYSCTL_DESCR("mbuf low water mark"),
		       sysctl_kern_mbuf, 0, &mblowat, 0,
		       CTL_KERN, KERN_MBUF, MBUF_MBLOWAT, CTL_EOL);
	sysctl_createv(&mbuf_sysctllog, 0, NULL, NULL,
		       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
		       CTLTYPE_INT, "mcllowat",
		       SYSCTL_DESCR("mbuf cluster low water mark"),
		       sysctl_kern_mbuf, 0, &mcllowat, 0,
		       CTL_KERN, KERN_MBUF, MBUF_MCLLOWAT, CTL_EOL);
	sysctl_createv(&mbuf_sysctllog, 0, NULL, NULL,
		       CTLFLAG_PERMANENT,
		       CTLTYPE_STRUCT, "stats",
		       SYSCTL_DESCR("mbuf allocation statistics"),
		       sysctl_kern_mbuf_stats, 0, NULL, 0,
		       CTL_KERN, KERN_MBUF, MBUF_STATS, CTL_EOL);
#ifdef MBUFTRACE
	sysctl_createv(&mbuf_sysctllog, 0, NULL, NULL,
		       CTLFLAG_PERMANENT,
		       CTLTYPE_STRUCT, "mowners",
		       SYSCTL_DESCR("Information about mbuf owners"),
		       sysctl_kern_mbuf_mowners, 0, NULL, 0,
		       CTL_KERN, KERN_MBUF, MBUF_MOWNERS, CTL_EOL);
#endif
	sysctl_createv(&mbuf_sysctllog, 0, NULL, NULL,
		       CTLFLAG_PERMANENT|CTLFLAG_READONLY,
		       CTLTYPE_INT, "nmbclusters_limit",
		       SYSCTL_DESCR("Limit of nmbclusters"),
		       sysctl_kern_mbuf, 0, NULL, 0,
		       CTL_KERN, KERN_MBUF, MBUF_NMBCLUSTERS_LIMIT, CTL_EOL);
}

static int
mb_ctor(void *arg, void *object, int flags)
{
	struct mbuf *m = object;

#ifdef POOL_VTOPHYS
	m->m_paddr = POOL_VTOPHYS(m);
#else
	m->m_paddr = M_PADDR_INVALID;
#endif
	return 0;
}

/*
 * Add mbuf to the end of a chain
 */
struct mbuf *
m_add(struct mbuf *c, struct mbuf *m)
{
	struct mbuf *n;

	if (c == NULL)
		return m;

	for (n = c; n->m_next != NULL; n = n->m_next)
		continue;
	n->m_next = m;
	return c;
}

struct mbuf *
m_get(int how, int type)
{
	struct mbuf *m;

	KASSERT(type != MT_FREE);

	m = pool_cache_get(mb_cache,
	    how == M_WAIT ? PR_WAITOK|PR_LIMITFAIL : PR_NOWAIT);
	if (m == NULL)
		return NULL;
	KASSERTMSG(((vaddr_t)m->m_dat & PAGE_MASK) + MLEN <= PAGE_SIZE,
	    "m=%p m->m_dat=%p"
	    " MLEN=%u PAGE_MASK=0x%x PAGE_SIZE=%u",
	    m, m->m_dat,
	    (unsigned)MLEN, (unsigned)PAGE_MASK, (unsigned)PAGE_SIZE);

	mbstat_type_add(type, 1);

	mowner_init(m, type);
	m->m_ext_ref = m; /* default */
	m->m_type = type;
	m->m_len = 0;
	m->m_next = NULL;
	m->m_nextpkt = NULL; /* default */
	m->m_data = m->m_dat;
	m->m_flags = 0; /* default */

	return m;
}

struct mbuf *
m_gethdr(int how, int type)
{
	struct mbuf *m;

	m = m_get(how, type);
	if (m == NULL)
		return NULL;

	m->m_data = m->m_pktdat;
	m->m_flags = M_PKTHDR;

	m_reset_rcvif(m);
	m->m_pkthdr.len = 0;
	m->m_pkthdr.csum_flags = 0;
	m->m_pkthdr.csum_data = 0;
	m->m_pkthdr.segsz = 0;
	m->m_pkthdr.ether_vtag = 0;
	m->m_pkthdr.pkthdr_flags = 0;
	SLIST_INIT(&m->m_pkthdr.tags);

	m->m_pkthdr.pattr_class = NULL;
	m->m_pkthdr.pattr_af = AF_UNSPEC;
	m->m_pkthdr.pattr_hdr = NULL;

	return m;
}

struct mbuf *
m_get_n(int how, int type, size_t alignbytes, size_t nbytes)
{
	struct mbuf *m;

	if (alignbytes > MCLBYTES || nbytes > MCLBYTES - alignbytes)
		return NULL;
	if ((m = m_get(how, type)) == NULL)
		return NULL;
	if (nbytes + alignbytes > MLEN) {
		m_clget(m, how);
		if ((m->m_flags & M_EXT) == 0) {
			m_free(m);
			return NULL;
		}
	}
	m->m_len = alignbytes + nbytes;
	m_adj(m, alignbytes);

	return m;
}

struct mbuf *
m_gethdr_n(int how, int type, size_t alignbytes, size_t nbytes)
{
	struct mbuf *m;

	if (nbytes > MCLBYTES || nbytes > MCLBYTES - alignbytes)
		return NULL;
	if ((m = m_gethdr(how, type)) == NULL)
		return NULL;
	if (alignbytes + nbytes > MHLEN) {
		m_clget(m, how);
		if ((m->m_flags & M_EXT) == 0) {
			m_free(m);
			return NULL;
		}
	}
	m->m_len = m->m_pkthdr.len = alignbytes + nbytes;
	m_adj(m, alignbytes);

	return m;
}

void
m_clget(struct mbuf *m, int how)
{
	m->m_ext_storage.ext_buf = (char *)pool_cache_get_paddr(mcl_cache,
	    how == M_WAIT ? (PR_WAITOK|PR_LIMITFAIL) : PR_NOWAIT,
	    &m->m_ext_storage.ext_paddr);

	if (m->m_ext_storage.ext_buf == NULL)
		return;

	KASSERTMSG((((vaddr_t)m->m_ext_storage.ext_buf & PAGE_MASK) + mclbytes
		<= PAGE_SIZE),
	    "m=%p m->m_ext_storage.ext_buf=%p"
	    " mclbytes=%u PAGE_MASK=0x%x PAGE_SIZE=%u",
	    m, m->m_dat,
	    (unsigned)mclbytes, (unsigned)PAGE_MASK, (unsigned)PAGE_SIZE);

	MCLINITREFERENCE(m);
	m->m_data = m->m_ext.ext_buf;
	m->m_flags = (m->m_flags & ~M_EXTCOPYFLAGS) |
	    M_EXT|M_EXT_CLUSTER|M_EXT_RW;
	m->m_ext.ext_size = MCLBYTES;
	m->m_ext.ext_free = NULL;
	m->m_ext.ext_arg = NULL;
	/* ext_paddr initialized above */

	mowner_ref(m, M_EXT|M_EXT_CLUSTER);
}

struct mbuf *
m_getcl(int how, int type, int flags)
{
	struct mbuf *mp;

	if ((flags & M_PKTHDR) != 0)
		mp = m_gethdr(how, type);
	else
		mp = m_get(how, type);

	if (mp == NULL)
		return NULL;

	MCLGET(mp, how);
	if ((mp->m_flags & M_EXT) != 0)
		return mp;

	m_free(mp);
	return NULL;
}

/*
 * Utility function for M_PREPEND. Do *NOT* use it directly.
 */
struct mbuf *
m_prepend(struct mbuf *m, int len, int how)
{
	struct mbuf *mn;

	if (__predict_false(len > MHLEN)) {
		panic("%s: len > MHLEN", __func__);
	}

	KASSERT(len != M_COPYALL);
	mn = m_get(how, m->m_type);
	if (mn == NULL) {
		m_freem(m);
		return NULL;
	}

	if (m->m_flags & M_PKTHDR) {
		m_move_pkthdr(mn, m);
	} else {
		MCLAIM(mn, m->m_owner);
	}
	mn->m_next = m;
	m = mn;

	if (m->m_flags & M_PKTHDR) {
		if (len < MHLEN)
			m_align(m, len);
	} else {
		if (len < MLEN)
			m_align(m, len);
	}

	m->m_len = len;
	return m;
}

struct mbuf *
m_copym(struct mbuf *m, int off, int len, int wait)
{
	/* Shallow copy on M_EXT. */
	return m_copy_internal(m, off, len, wait, false);
}

struct mbuf *
m_dup(struct mbuf *m, int off, int len, int wait)
{
	/* Deep copy. */
	return m_copy_internal(m, off, len, wait, true);
}

static inline int
m_copylen(int len, int copylen)
{
	return (len == M_COPYALL) ? copylen : uimin(len, copylen);
}

static struct mbuf *
m_copy_internal(struct mbuf *m, int off0, int len, int wait, bool deep)
{
	struct mbuf *m0 __diagused = m;
	int len0 __diagused = len;
	struct mbuf *n, **np;
	int off = off0;
	struct mbuf *top;
	int copyhdr = 0;

	if (off < 0 || (len != M_COPYALL && len < 0))
		panic("%s: off %d, len %d", __func__, off, len);
	if (off == 0 && m->m_flags & M_PKTHDR)
		copyhdr = 1;
	while (off > 0) {
		if (m == NULL)
			panic("%s: m == NULL, off %d", __func__, off);
		if (off < m->m_len)
			break;
		off -= m->m_len;
		m = m->m_next;
	}

	np = &top;
	top = NULL;
	while (len == M_COPYALL || len > 0) {
		if (m == NULL) {
			if (len != M_COPYALL)
				panic("%s: m == NULL, len %d [!COPYALL]",
				    __func__, len);
			break;
		}

		n = m_get(wait, m->m_type);
		*np = n;
		if (n == NULL)
			goto nospace;
		MCLAIM(n, m->m_owner);

		if (copyhdr) {
			m_copy_pkthdr(n, m);
			if (len == M_COPYALL)
				n->m_pkthdr.len -= off0;
			else
				n->m_pkthdr.len = len;
			copyhdr = 0;
		}
		n->m_len = m_copylen(len, m->m_len - off);

		if (m->m_flags & M_EXT) {
			if (!deep) {
				n->m_data = m->m_data + off;
				MCLADDREFERENCE(m, n);
			} else {
				/*
				 * We don't care if MCLGET fails. n->m_len is
				 * recomputed and handles that.
				 */
				MCLGET(n, wait);
				n->m_len = 0;
				n->m_len = M_TRAILINGSPACE(n);
				n->m_len = m_copylen(len, n->m_len);
				n->m_len = uimin(n->m_len, m->m_len - off);
				memcpy(mtod(n, void *), mtod(m, char *) + off,
				    (unsigned)n->m_len);
			}
		} else {
			memcpy(mtod(n, void *), mtod(m, char *) + off,
			    (unsigned)n->m_len);
		}

		if (len != M_COPYALL)
			len -= n->m_len;
		off += n->m_len;

		KASSERTMSG(off <= m->m_len,
		    "m=%p m->m_len=%d off=%d len=%d m0=%p off0=%d len0=%d",
		    m, m->m_len, off, len, m0, off0, len0);

		if (off == m->m_len) {
			m = m->m_next;
			off = 0;
		}
		np = &n->m_next;
	}

	return top;

nospace:
	m_freem(top);
	return NULL;
}

/*
 * Copy an entire packet, including header (which must be present).
 * An optimization of the common case 'm_copym(m, 0, M_COPYALL, how)'.
 */
struct mbuf *
m_copypacket(struct mbuf *m, int how)
{
	struct mbuf *top, *n, *o;

	if (__predict_false((m->m_flags & M_PKTHDR) == 0)) {
		panic("%s: no header (m = %p)", __func__, m);
	}

	n = m_get(how, m->m_type);
	top = n;
	if (!n)
		goto nospace;

	MCLAIM(n, m->m_owner);
	m_copy_pkthdr(n, m);
	n->m_len = m->m_len;
	if (m->m_flags & M_EXT) {
		n->m_data = m->m_data;
		MCLADDREFERENCE(m, n);
	} else {
		memcpy(mtod(n, char *), mtod(m, char *), n->m_len);
	}

	m = m->m_next;
	while (m) {
		o = m_get(how, m->m_type);
		if (!o)
			goto nospace;

		MCLAIM(o, m->m_owner);
		n->m_next = o;
		n = n->m_next;

		n->m_len = m->m_len;
		if (m->m_flags & M_EXT) {
			n->m_data = m->m_data;
			MCLADDREFERENCE(m, n);
		} else {
			memcpy(mtod(n, char *), mtod(m, char *), n->m_len);
		}

		m = m->m_next;
	}
	return top;

nospace:
	m_freem(top);
	return NULL;
}

void
m_copydata(struct mbuf *m, int off, int len, void *cp)
{
	unsigned int count;
	struct mbuf *m0 = m;
	int len0 = len;
	int off0 = off;
	void *cp0 = cp;

	KASSERT(len != M_COPYALL);
	if (off < 0 || len < 0)
		panic("m_copydata: off %d, len %d", off, len);
	while (off > 0) {
		if (m == NULL)
			panic("m_copydata(%p,%d,%d,%p): m=NULL, off=%d (%d)",
			    m0, len0, off0, cp0, off, off0 - off);
		if (off < m->m_len)
			break;
		off -= m->m_len;
		m = m->m_next;
	}
	while (len > 0) {
		if (m == NULL)
			panic("m_copydata(%p,%d,%d,%p): "
			    "m=NULL, off=%d (%d), len=%d (%d)",
			    m0, len0, off0, cp0,
			    off, off0 - off, len, len0 - len);
		count = uimin(m->m_len - off, len);
		memcpy(cp, mtod(m, char *) + off, count);
		len -= count;
		cp = (char *)cp + count;
		off = 0;
		m = m->m_next;
	}
}

/*
 * Concatenate mbuf chain n to m.
 * n might be copied into m (when n->m_len is small), therefore data portion of
 * n could be copied into an mbuf of different mbuf type.
 * Any m_pkthdr is not updated.
 */
void
m_cat(struct mbuf *m, struct mbuf *n)
{

	while (m->m_next)
		m = m->m_next;
	while (n) {
		if (M_READONLY(m) || n->m_len > M_TRAILINGSPACE(m)) {
			/* just join the two chains */
			m->m_next = n;
			return;
		}
		/* splat the data from one into the other */
		memcpy(mtod(m, char *) + m->m_len, mtod(n, void *),
		    (u_int)n->m_len);
		m->m_len += n->m_len;
		n = m_free(n);
	}
}

void
m_adj(struct mbuf *mp, int req_len)
{
	int len = req_len;
	struct mbuf *m;
	int count;

	if ((m = mp) == NULL)
		return;
	if (len >= 0) {
		/*
		 * Trim from head.
		 */
		while (m != NULL && len > 0) {
			if (m->m_len <= len) {
				len -= m->m_len;
				m->m_len = 0;
				m = m->m_next;
			} else {
				m->m_len -= len;
				m->m_data += len;
				len = 0;
			}
		}
		if (mp->m_flags & M_PKTHDR)
			mp->m_pkthdr.len -= (req_len - len);
	} else {
		/*
		 * Trim from tail.  Scan the mbuf chain,
		 * calculating its length and finding the last mbuf.
		 * If the adjustment only affects this mbuf, then just
		 * adjust and return.  Otherwise, rescan and truncate
		 * after the remaining size.
		 */
		len = -len;
		count = 0;
		for (;;) {
			count += m->m_len;
			if (m->m_next == NULL)
				break;
			m = m->m_next;
		}
		if (m->m_len >= len) {
			m->m_len -= len;
			if (mp->m_flags & M_PKTHDR)
				mp->m_pkthdr.len -= len;
			return;
		}

		count -= len;
		if (count < 0)
			count = 0;

		/*
		 * Correct length for chain is "count".
		 * Find the mbuf with last data, adjust its length,
		 * and toss data from remaining mbufs on chain.
		 */
		m = mp;
		if (m->m_flags & M_PKTHDR)
			m->m_pkthdr.len = count;
		for (; m; m = m->m_next) {
			if (m->m_len >= count) {
				m->m_len = count;
				break;
			}
			count -= m->m_len;
		}
		if (m) {
			while (m->m_next)
				(m = m->m_next)->m_len = 0;
		}
	}
}

/*
 * m_ensure_contig: rearrange an mbuf chain that given length of bytes
 * would be contiguous and in the data area of an mbuf (therefore, mtod()
 * would work for a structure of given length).
 *
 * => On success, returns true and the resulting mbuf chain; false otherwise.
 * => The mbuf chain may change, but is always preserved valid.
 */
bool
m_ensure_contig(struct mbuf **m0, int len)
{
	struct mbuf *n = *m0, *m;
	size_t count, space;

	KASSERT(len != M_COPYALL);
	/*
	 * If first mbuf has no cluster, and has room for len bytes
	 * without shifting current data, pullup into it,
	 * otherwise allocate a new mbuf to prepend to the chain.
	 */
	if ((n->m_flags & M_EXT) == 0 &&
	    n->m_data + len < &n->m_dat[MLEN] && n->m_next) {
		if (n->m_len >= len) {
			return true;
		}
		m = n;
		n = n->m_next;
		len -= m->m_len;
	} else {
		if (len > MHLEN) {
			return false;
		}
		m = m_get(M_DONTWAIT, n->m_type);
		if (m == NULL) {
			return false;
		}
		MCLAIM(m, n->m_owner);
		if (n->m_flags & M_PKTHDR) {
			m_move_pkthdr(m, n);
		}
	}
	space = &m->m_dat[MLEN] - (m->m_data + m->m_len);
	do {
		count = MIN(MIN(MAX(len, max_protohdr), space), n->m_len);
		memcpy(mtod(m, char *) + m->m_len, mtod(n, void *),
		  (unsigned)count);
		len -= count;
		m->m_len += count;
		n->m_len -= count;
		space -= count;
		if (n->m_len)
			n->m_data += count;
		else
			n = m_free(n);
	} while (len > 0 && n);

	m->m_next = n;
	*m0 = m;

	return len <= 0;
}

/*
 * m_pullup: same as m_ensure_contig(), but destroys mbuf chain on error.
 */
struct mbuf *
m_pullup(struct mbuf *n, int len)
{
	struct mbuf *m = n;

	KASSERT(len != M_COPYALL);
	if (!m_ensure_contig(&m, len)) {
		KASSERT(m != NULL);
		m_freem(m);
		m = NULL;
	}
	return m;
}

/*
 * ensure that [off, off + len) is contiguous on the mbuf chain "m".
 * packet chain before "off" is kept untouched.
 * if offp == NULL, the target will start at <retval, 0> on resulting chain.
 * if offp != NULL, the target will start at <retval, *offp> on resulting chain.
 *
 * on error return (NULL return value), original "m" will be freed.
 *
 * XXX M_TRAILINGSPACE/M_LEADINGSPACE on shared cluster (sharedcluster)
 */
struct mbuf *
m_pulldown(struct mbuf *m, int off, int len, int *offp)
{
	struct mbuf *n, *o;
	int hlen, tlen, olen;
	int sharedcluster;

	/* Check invalid arguments. */
	if (m == NULL)
		panic("%s: m == NULL", __func__);
	if (len > MCLBYTES) {
		m_freem(m);
		return NULL;
	}

	n = m;
	while (n != NULL && off > 0) {
		if (n->m_len > off)
			break;
		off -= n->m_len;
		n = n->m_next;
	}
	/* Be sure to point non-empty mbuf. */
	while (n != NULL && n->m_len == 0)
		n = n->m_next;
	if (!n) {
		m_freem(m);
		return NULL;	/* mbuf chain too short */
	}

	sharedcluster = M_READONLY(n);

	/*
	 * The target data is on <n, off>. If we got enough data on the mbuf
	 * "n", we're done.
	 */
#ifdef __NO_STRICT_ALIGNMENT
	if ((off == 0 || offp) && len <= n->m_len - off && !sharedcluster)
#else
	if ((off == 0 || offp) && len <= n->m_len - off && !sharedcluster &&
	    ALIGNED_POINTER((mtod(n, char *) + off), uint32_t))
#endif
		goto ok;

	/*
	 * When (len <= n->m_len - off) and (off != 0), it is a special case.
	 * Len bytes from <n, off> sit in single mbuf, but the caller does
	 * not like the starting position (off).
	 *
	 * Chop the current mbuf into two pieces, set off to 0.
	 */
	if (len <= n->m_len - off) {
		struct mbuf *mlast;

		o = m_dup(n, off, n->m_len - off, M_DONTWAIT);
		if (o == NULL) {
			m_freem(m);
			return NULL;	/* ENOBUFS */
		}
		KASSERTMSG(o->m_len >= len, "o=%p o->m_len=%d len=%d",
		    o, o->m_len, len);
		for (mlast = o; mlast->m_next != NULL; mlast = mlast->m_next)
			;
		n->m_len = off;
		mlast->m_next = n->m_next;
		n->m_next = o;
		n = o;
		off = 0;
		goto ok;
	}

	/*
	 * We need to take hlen from <n, off> and tlen from <n->m_next, 0>,
	 * and construct contiguous mbuf with m_len == len.
	 *
	 * Note that hlen + tlen == len, and tlen > 0.
	 */
	hlen = n->m_len - off;
	tlen = len - hlen;

	/*
	 * Ensure that we have enough trailing data on mbuf chain. If not,
	 * we can do nothing about the chain.
	 */
	olen = 0;
	for (o = n->m_next; o != NULL; o = o->m_next)
		olen += o->m_len;
	if (hlen + olen < len) {
		m_freem(m);
		return NULL;	/* mbuf chain too short */
	}

	/*
	 * Easy cases first. We need to use m_copydata() to get data from
	 * <n->m_next, 0>.
	 */
	if ((off == 0 || offp) && M_TRAILINGSPACE(n) >= tlen &&
	    !sharedcluster) {
		m_copydata(n->m_next, 0, tlen, mtod(n, char *) + n->m_len);
		n->m_len += tlen;
		m_adj(n->m_next, tlen);
		goto ok;
	}
	if ((off == 0 || offp) && M_LEADINGSPACE(n->m_next) >= hlen &&
#ifndef __NO_STRICT_ALIGNMENT
	    ALIGNED_POINTER((n->m_next->m_data - hlen), uint32_t) &&
#endif
	    !sharedcluster && n->m_next->m_len >= tlen) {
		n->m_next->m_data -= hlen;
		n->m_next->m_len += hlen;
		memcpy(mtod(n->m_next, void *), mtod(n, char *) + off, hlen);
		n->m_len -= hlen;
		n = n->m_next;
		off = 0;
		goto ok;
	}

	/*
	 * Now, we need to do the hard way. Don't copy as there's no room
	 * on both ends.
	 */
	o = m_get(M_DONTWAIT, m->m_type);
	if (o && len > MLEN) {
		MCLGET(o, M_DONTWAIT);
		if ((o->m_flags & M_EXT) == 0) {
			m_free(o);
			o = NULL;
		}
	}
	if (!o) {
		m_freem(m);
		return NULL;	/* ENOBUFS */
	}
	/* get hlen from <n, off> into <o, 0> */
	o->m_len = hlen;
	memcpy(mtod(o, void *), mtod(n, char *) + off, hlen);
	n->m_len -= hlen;
	/* get tlen from <n->m_next, 0> into <o, hlen> */
	m_copydata(n->m_next, 0, tlen, mtod(o, char *) + o->m_len);
	o->m_len += tlen;
	m_adj(n->m_next, tlen);
	o->m_next = n->m_next;
	n->m_next = o;
	n = o;
	off = 0;

ok:
	if (offp)
		*offp = off;
	return n;
}

/*
 * Like m_pullup(), except a new mbuf is always allocated, and we allow
 * the amount of empty space before the data in the new mbuf to be specified
 * (in the event that the caller expects to prepend later).
 */
struct mbuf *
m_copyup(struct mbuf *n, int len, int dstoff)
{
	struct mbuf *m;
	int count, space;

	KASSERT(len != M_COPYALL);
	if (len > ((int)MHLEN - dstoff))
		goto bad;
	m = m_get(M_DONTWAIT, n->m_type);
	if (m == NULL)
		goto bad;
	MCLAIM(m, n->m_owner);
	if (n->m_flags & M_PKTHDR) {
		m_move_pkthdr(m, n);
	}
	m->m_data += dstoff;
	space = &m->m_dat[MLEN] - (m->m_data + m->m_len);
	do {
		count = uimin(uimin(uimax(len, max_protohdr), space), n->m_len);
		memcpy(mtod(m, char *) + m->m_len, mtod(n, void *),
		    (unsigned)count);
		len -= count;
		m->m_len += count;
		n->m_len -= count;
		space -= count;
		if (n->m_len)
			n->m_data += count;
		else
			n = m_free(n);
	} while (len > 0 && n);
	if (len > 0) {
		(void) m_free(m);
		goto bad;
	}
	m->m_next = n;
	return m;
 bad:
	m_freem(n);
	return NULL;
}

struct mbuf *
m_split(struct mbuf *m0, int len, int wait)
{
	return m_split_internal(m0, len, wait, true);
}

static struct mbuf *
m_split_internal(struct mbuf *m0, int len0, int wait, bool copyhdr)
{
	struct mbuf *m, *n;
	unsigned len = len0, remain, len_save;

	KASSERT(len0 != M_COPYALL);
	for (m = m0; m && len > m->m_len; m = m->m_next)
		len -= m->m_len;
	if (m == NULL)
		return NULL;

	remain = m->m_len - len;
	if (copyhdr && (m0->m_flags & M_PKTHDR)) {
		n = m_gethdr(wait, m0->m_type);
		if (n == NULL)
			return NULL;

		MCLAIM(n, m0->m_owner);
		m_copy_rcvif(n, m0);
		n->m_pkthdr.len = m0->m_pkthdr.len - len0;
		len_save = m0->m_pkthdr.len;
		m0->m_pkthdr.len = len0;

		if (m->m_flags & M_EXT)
			goto extpacket;

		if (remain > MHLEN) {
			/* m can't be the lead packet */
			m_align(n, 0);
			n->m_len = 0;
			n->m_next = m_split(m, len, wait);
			if (n->m_next == NULL) {
				(void)m_free(n);
				m0->m_pkthdr.len = len_save;
				return NULL;
			}
			return n;
		} else {
			m_align(n, remain);
		}
	} else if (remain == 0) {
		n = m->m_next;
		m->m_next = NULL;
		return n;
	} else {
		n = m_get(wait, m->m_type);
		if (n == NULL)
			return NULL;
		MCLAIM(n, m->m_owner);
		m_align(n, remain);
	}

extpacket:
	if (m->m_flags & M_EXT) {
		n->m_data = m->m_data + len;
		MCLADDREFERENCE(m, n);
	} else {
		memcpy(mtod(n, void *), mtod(m, char *) + len, remain);
	}

	n->m_len = remain;
	m->m_len = len;
	n->m_next = m->m_next;
	m->m_next = NULL;
	return n;
}

/*
 * Routine to copy from device local memory into mbufs.
 */
struct mbuf *
m_devget(char *buf, int totlen, int off, struct ifnet *ifp)
{
	struct mbuf *m;
	struct mbuf *top = NULL, **mp = &top;
	char *cp, *epkt;
	int len;

	cp = buf;
	epkt = cp + totlen;
	if (off) {
		/*
		 * If 'off' is non-zero, packet is trailer-encapsulated,
		 * so we have to skip the type and length fields.
		 */
		cp += off + 2 * sizeof(uint16_t);
		totlen -= 2 * sizeof(uint16_t);
	}

	m = m_gethdr(M_DONTWAIT, MT_DATA);
	if (m == NULL)
		return NULL;
	m_set_rcvif(m, ifp);
	m->m_pkthdr.len = totlen;
	m->m_len = MHLEN;

	while (totlen > 0) {
		if (top) {
			m = m_get(M_DONTWAIT, MT_DATA);
			if (m == NULL) {
				m_freem(top);
				return NULL;
			}
			m->m_len = MLEN;
		}

		len = uimin(totlen, epkt - cp);

		if (len >= MINCLSIZE) {
			MCLGET(m, M_DONTWAIT);
			if ((m->m_flags & M_EXT) == 0) {
				m_free(m);
				m_freem(top);
				return NULL;
			}
			m->m_len = len = uimin(len, MCLBYTES);
		} else {
			/*
			 * Place initial small packet/header at end of mbuf.
			 */
			if (len < m->m_len) {
				if (top == 0 && len + max_linkhdr <= m->m_len)
					m->m_data += max_linkhdr;
				m->m_len = len;
			} else
				len = m->m_len;
		}

		memcpy(mtod(m, void *), cp, (size_t)len);

		cp += len;
		*mp = m;
		mp = &m->m_next;
		totlen -= len;
		if (cp == epkt)
			cp = buf;
	}

	return top;
}

/*
 * Copy data from a buffer back into the indicated mbuf chain,
 * starting "off" bytes from the beginning, extending the mbuf
 * chain if necessary.
 */
void
m_copyback(struct mbuf *m0, int off, int len, const void *cp)
{
#if defined(DEBUG)
	struct mbuf *origm = m0;
	int error;
#endif

	if (m0 == NULL)
		return;

#if defined(DEBUG)
	error =
#endif
	m_copyback_internal(&m0, off, len, cp, CB_COPYBACK|CB_EXTEND,
	    M_DONTWAIT);

#if defined(DEBUG)
	if (error != 0 || (m0 != NULL && origm != m0))
		panic("m_copyback");
#endif
}

struct mbuf *
m_copyback_cow(struct mbuf *m0, int off, int len, const void *cp, int how)
{
	int error;

	/* don't support chain expansion */
	KASSERT(len != M_COPYALL);
	KDASSERT(off + len <= m_length(m0));

	error = m_copyback_internal(&m0, off, len, cp, CB_COPYBACK|CB_COW,
	    how);
	if (error) {
		/*
		 * no way to recover from partial success.
		 * just free the chain.
		 */
		m_freem(m0);
		return NULL;
	}
	return m0;
}

int
m_makewritable(struct mbuf **mp, int off, int len, int how)
{
	int error;
#if defined(DEBUG)
	int origlen = m_length(*mp);
#endif

	error = m_copyback_internal(mp, off, len, NULL, CB_PRESERVE|CB_COW,
	    how);
	if (error)
		return error;

#if defined(DEBUG)
	int reslen = 0;
	for (struct mbuf *n = *mp; n; n = n->m_next)
		reslen += n->m_len;
	if (origlen != reslen)
		panic("m_makewritable: length changed");
	if (((*mp)->m_flags & M_PKTHDR) != 0 && reslen != (*mp)->m_pkthdr.len)
		panic("m_makewritable: inconsist");
#endif

	return 0;
}

static int
m_copyback_internal(struct mbuf **mp0, int off, int len, const void *vp,
    int flags, int how)
{
	int mlen;
	struct mbuf *m, *n;
	struct mbuf **mp;
	int totlen = 0;
	const char *cp = vp;

	KASSERT(mp0 != NULL);
	KASSERT(*mp0 != NULL);
	KASSERT((flags & CB_PRESERVE) == 0 || cp == NULL);
	KASSERT((flags & CB_COPYBACK) == 0 || cp != NULL);

	if (len == M_COPYALL)
		len = m_length(*mp0) - off;

	/*
	 * we don't bother to update "totlen" in the case of CB_COW,
	 * assuming that CB_EXTEND and CB_COW are exclusive.
	 */

	KASSERT((~flags & (CB_EXTEND|CB_COW)) != 0);

	mp = mp0;
	m = *mp;
	while (off > (mlen = m->m_len)) {
		off -= mlen;
		totlen += mlen;
		if (m->m_next == NULL) {
			int tspace;
extend:
			if ((flags & CB_EXTEND) == 0)
				goto out;

			/*
			 * try to make some space at the end of "m".
			 */

			mlen = m->m_len;
			if (off + len >= MINCLSIZE &&
			    (m->m_flags & M_EXT) == 0 && m->m_len == 0) {
				MCLGET(m, how);
			}
			tspace = M_TRAILINGSPACE(m);
			if (tspace > 0) {
				tspace = uimin(tspace, off + len);
				KASSERT(tspace > 0);
				memset(mtod(m, char *) + m->m_len, 0,
				    uimin(off, tspace));
				m->m_len += tspace;
				off += mlen;
				totlen -= mlen;
				continue;
			}

			/*
			 * need to allocate an mbuf.
			 */

			if (off + len >= MINCLSIZE) {
				n = m_getcl(how, m->m_type, 0);
			} else {
				n = m_get(how, m->m_type);
			}
			if (n == NULL) {
				goto out;
			}
			n->m_len = uimin(M_TRAILINGSPACE(n), off + len);
			memset(mtod(n, char *), 0, uimin(n->m_len, off));
			m->m_next = n;
		}
		mp = &m->m_next;
		m = m->m_next;
	}
	while (len > 0) {
		mlen = m->m_len - off;
		if (mlen != 0 && M_READONLY(m)) {
			/*
			 * This mbuf is read-only. Allocate a new writable
			 * mbuf and try again.
			 */
			char *datap;
			int eatlen;

			KASSERT((flags & CB_COW) != 0);

			/*
			 * if we're going to write into the middle of
			 * a mbuf, split it first.
			 */
			if (off > 0) {
				n = m_split_internal(m, off, how, false);
				if (n == NULL)
					goto enobufs;
				m->m_next = n;
				mp = &m->m_next;
				m = n;
				off = 0;
				continue;
			}

			/*
			 * XXX TODO coalesce into the trailingspace of
			 * the previous mbuf when possible.
			 */

			/*
			 * allocate a new mbuf.  copy packet header if needed.
			 */
			n = m_get(how, m->m_type);
			if (n == NULL)
				goto enobufs;
			MCLAIM(n, m->m_owner);
			if (off == 0 && (m->m_flags & M_PKTHDR) != 0) {
				m_move_pkthdr(n, m);
				n->m_len = MHLEN;
			} else {
				if (len >= MINCLSIZE)
					MCLGET(n, M_DONTWAIT);
				n->m_len =
				    (n->m_flags & M_EXT) ? MCLBYTES : MLEN;
			}
			if (n->m_len > len)
				n->m_len = len;

			/*
			 * free the region which has been overwritten.
			 * copying data from old mbufs if requested.
			 */
			if (flags & CB_PRESERVE)
				datap = mtod(n, char *);
			else
				datap = NULL;
			eatlen = n->m_len;
			while (m != NULL && M_READONLY(m) &&
			    n->m_type == m->m_type && eatlen > 0) {
				mlen = uimin(eatlen, m->m_len);
				if (datap) {
					m_copydata(m, 0, mlen, datap);
					datap += mlen;
				}
				m->m_data += mlen;
				m->m_len -= mlen;
				eatlen -= mlen;
				if (m->m_len == 0)
					*mp = m = m_free(m);
			}
			if (eatlen > 0)
				n->m_len -= eatlen;
			n->m_next = m;
			*mp = m = n;
			continue;
		}
		mlen = uimin(mlen, len);
		if (flags & CB_COPYBACK) {
			memcpy(mtod(m, char *) + off, cp, (unsigned)mlen);
			cp += mlen;
		}
		len -= mlen;
		mlen += off;
		off = 0;
		totlen += mlen;
		if (len == 0)
			break;
		if (m->m_next == NULL) {
			goto extend;
		}
		mp = &m->m_next;
		m = m->m_next;
	}

out:
	if (((m = *mp0)->m_flags & M_PKTHDR) && (m->m_pkthdr.len < totlen)) {
		KASSERT((flags & CB_EXTEND) != 0);
		m->m_pkthdr.len = totlen;
	}

	return 0;

enobufs:
	return ENOBUFS;
}

/*
 * Compress the mbuf chain. Return the new mbuf chain on success, NULL on
 * failure. The first mbuf is preserved, and on success the pointer returned
 * is the same as the one passed.
 */
struct mbuf *
m_defrag(struct mbuf *m, int how)
{
	struct mbuf *m0, *mn, *n;
	int sz;

	KASSERT((m->m_flags & M_PKTHDR) != 0);

	if (m->m_next == NULL)
		return m;

	/* Defrag to single mbuf if at all possible */
	if ((m->m_flags & M_EXT) == 0 && m->m_pkthdr.len <= MCLBYTES) {
		if (m->m_pkthdr.len <= MHLEN) {
			if (M_TRAILINGSPACE(m) < (m->m_pkthdr.len - m->m_len)) {
				KASSERTMSG(M_LEADINGSPACE(m) +
				    M_TRAILINGSPACE(m) >=
				    (m->m_pkthdr.len - m->m_len),
				    "too small leading %d trailing %d ro? %d"
				    " pkthdr.len %d mlen %d",
				    (int)M_LEADINGSPACE(m),
				    (int)M_TRAILINGSPACE(m),
				    M_READONLY(m),
				    m->m_pkthdr.len, m->m_len);

				memmove(m->m_pktdat, m->m_data, m->m_len);
				m->m_data = m->m_pktdat;

				KASSERT(M_TRAILINGSPACE(m) >=
				    (m->m_pkthdr.len - m->m_len));
			}
		} else {
			/* Must copy data before adding cluster */
			m0 = m_get(how, MT_DATA);
			if (m0 == NULL)
				return NULL;
			KASSERTMSG(m->m_len <= MHLEN,
			    "m=%p m->m_len=%d MHLEN=%u",
			    m, m->m_len, (unsigned)MHLEN);
			m_copydata(m, 0, m->m_len, mtod(m0, void *));

			MCLGET(m, how);
			if ((m->m_flags & M_EXT) == 0) {
				m_free(m0);
				return NULL;
			}
			memcpy(m->m_data, mtod(m0, void *), m->m_len);
			m_free(m0);
		}
		KASSERTMSG(M_TRAILINGSPACE(m) >= (m->m_pkthdr.len - m->m_len),
		    "m=%p M_TRAILINGSPACE(m)=%zd m->m_pkthdr.len=%d"
		    " m->m_len=%d",
		    m, M_TRAILINGSPACE(m), m->m_pkthdr.len, m->m_len);
		m_copydata(m->m_next, 0, m->m_pkthdr.len - m->m_len,
			    mtod(m, char *) + m->m_len);
		m->m_len = m->m_pkthdr.len;
		m_freem(m->m_next);
		m->m_next = NULL;
		return m;
	}

	m0 = m_get(how, MT_DATA);
	if (m0 == NULL)
		return NULL;
	mn = m0;

	sz = m->m_pkthdr.len - m->m_len;
	KASSERT(sz >= 0);

	do {
		if (sz > MLEN) {
			MCLGET(mn, how);
			if ((mn->m_flags & M_EXT) == 0) {
				m_freem(m0);
				return NULL;
			}
		}

		mn->m_len = MIN(sz, MCLBYTES);

		m_copydata(m, m->m_pkthdr.len - sz, mn->m_len,
		     mtod(mn, void *));

		sz -= mn->m_len;

		if (sz > 0) {
			/* need more mbufs */
			n = m_get(how, MT_DATA);
			if (n == NULL) {
				m_freem(m0);
				return NULL;
			}

			mn->m_next = n;
			mn = n;
		}
	} while (sz > 0);

	m_freem(m->m_next);
	m->m_next = m0;

	return m;
}

void
m_remove_pkthdr(struct mbuf *m)
{
	KASSERT(m->m_flags & M_PKTHDR);

	m_tag_delete_chain(m);
	m->m_flags &= ~M_PKTHDR;
	memset(&m->m_pkthdr, 0, sizeof(m->m_pkthdr));
}

void
m_copy_pkthdr(struct mbuf *to, struct mbuf *from)
{
	KASSERT((to->m_flags & M_EXT) == 0);
	KASSERT((to->m_flags & M_PKTHDR) == 0 ||
	    SLIST_FIRST(&to->m_pkthdr.tags) == NULL);
	KASSERT((from->m_flags & M_PKTHDR) != 0);

	to->m_pkthdr = from->m_pkthdr;
	to->m_flags = from->m_flags & M_COPYFLAGS;
	to->m_data = to->m_pktdat;

	SLIST_INIT(&to->m_pkthdr.tags);
	m_tag_copy_chain(to, from);
}

void
m_move_pkthdr(struct mbuf *to, struct mbuf *from)
{
	KASSERT((to->m_flags & M_EXT) == 0);
	KASSERT((to->m_flags & M_PKTHDR) == 0 ||
	    SLIST_FIRST(&to->m_pkthdr.tags) == NULL);
	KASSERT((from->m_flags & M_PKTHDR) != 0);

	to->m_pkthdr = from->m_pkthdr;
	to->m_flags = from->m_flags & M_COPYFLAGS;
	to->m_data = to->m_pktdat;

	from->m_flags &= ~M_PKTHDR;
}

/*
 * Set the m_data pointer of a newly-allocated mbuf to place an object of the
 * specified size at the end of the mbuf, longword aligned.
 */
void
m_align(struct mbuf *m, int len)
{
	int buflen, adjust;

	KASSERT(len != M_COPYALL);
	KASSERTMSG(M_LEADINGSPACE(m) == 0, "m=%p M_LEADINGSPACE(m)=%zd",
	    m, M_LEADINGSPACE(m));

	buflen = M_BUFSIZE(m);

	KASSERTMSG(len <= buflen, "m=%p len=%d buflen=%d", m, len, buflen);
	adjust = buflen - len;
	m->m_data += adjust &~ (sizeof(long)-1);
}

/*
 * Apply function f to the data in an mbuf chain starting "off" bytes from the
 * beginning, continuing for "len" bytes.
 */
int
m_apply(struct mbuf *m, int off, int len,
    int (*f)(void *, void *, unsigned int), void *arg)
{
	unsigned int count;
	int rval;

	KASSERT(len != M_COPYALL);
	KASSERT(len >= 0);
	KASSERT(off >= 0);

	while (off > 0) {
		KASSERT(m != NULL);
		if (off < m->m_len)
			break;
		off -= m->m_len;
		m = m->m_next;
	}
	while (len > 0) {
		KASSERT(m != NULL);
		count = uimin(m->m_len - off, len);

		rval = (*f)(arg, mtod(m, char *) + off, count);
		if (rval)
			return rval;

		len -= count;
		off = 0;
		m = m->m_next;
	}

	return 0;
}

/*
 * Return a pointer to mbuf/offset of location in mbuf chain.
 */
struct mbuf *
m_getptr(struct mbuf *m, int loc, int *off)
{

	while (loc >= 0) {
		/* Normal end of search */
		if (m->m_len > loc) {
			*off = loc;
			return m;
		}

		loc -= m->m_len;

		if (m->m_next == NULL) {
			if (loc == 0) {
				/* Point at the end of valid data */
				*off = m->m_len;
				return m;
			}
			return NULL;
		} else {
			m = m->m_next;
		}
	}

	return NULL;
}

/*
 * Release a reference to the mbuf external storage.
 *
 * => free the mbuf m itself as well.
 */
static void
m_ext_free(struct mbuf *m)
{
	const bool embedded = MEXT_ISEMBEDDED(m);
	bool dofree = true;
	u_int refcnt;

	KASSERT((m->m_flags & M_EXT) != 0);
	KASSERT(MEXT_ISEMBEDDED(m->m_ext_ref));
	KASSERT((m->m_ext_ref->m_flags & M_EXT) != 0);
	KASSERT((m->m_flags & M_EXT_CLUSTER) ==
	    (m->m_ext_ref->m_flags & M_EXT_CLUSTER));

	if (__predict_false(m->m_type == MT_FREE)) {
		panic("mbuf %p already freed", m);
	}

	if (__predict_true(m->m_ext.ext_refcnt == 1)) {
		refcnt = m->m_ext.ext_refcnt = 0;
	} else {
		membar_release();
		refcnt = atomic_dec_uint_nv(&m->m_ext.ext_refcnt);
	}

	if (refcnt > 0) {
		if (embedded) {
			/*
			 * other mbuf's m_ext_ref still points to us.
			 */
			dofree = false;
		} else {
			m->m_ext_ref = m;
		}
	} else {
		/*
		 * dropping the last reference
		 */
		membar_acquire();
		if (!embedded) {
			m->m_ext.ext_refcnt++; /* XXX */
			m_ext_free(m->m_ext_ref);
			m->m_ext_ref = m;
		} else if ((m->m_flags & M_EXT_CLUSTER) != 0) {
			pool_cache_put_paddr(mcl_cache,
			    m->m_ext.ext_buf, m->m_ext.ext_paddr);
		} else if (m->m_ext.ext_free) {
			(*m->m_ext.ext_free)(m,
			    m->m_ext.ext_buf, m->m_ext.ext_size,
			    m->m_ext.ext_arg);
			/*
			 * 'm' is already freed by the ext_free callback.
			 */
			dofree = false;
		} else {
			free(m->m_ext.ext_buf, 0);
		}
	}

	if (dofree) {
		m->m_type = MT_FREE;
		m->m_data = NULL;
		pool_cache_put(mb_cache, m);
	}
}

/*
 * Free a single mbuf and associated external storage. Return the
 * successor, if any.
 */
struct mbuf *
m_free(struct mbuf *m)
{
	struct mbuf *n;

	mowner_revoke(m, 1, m->m_flags);
	mbstat_type_add(m->m_type, -1);

	if (m->m_flags & M_PKTHDR)
		m_tag_delete_chain(m);

	n = m->m_next;

	if (m->m_flags & M_EXT) {
		m_ext_free(m);
	} else {
		if (__predict_false(m->m_type == MT_FREE)) {
			panic("mbuf %p already freed", m);
		}
		m->m_type = MT_FREE;
		m->m_data = NULL;
		pool_cache_put(mb_cache, m);
	}

	return n;
}

void
m_freem(struct mbuf *m)
{
	if (m == NULL)
		return;
	do {
		m = m_free(m);
	} while (m);
}

#if defined(DDB)
void
m_print(const struct mbuf *m, const char *modif, void (*pr)(const char *, ...))
{
	char ch;
	bool opt_c = false;
	bool opt_d = false;
#if NETHER > 0
	bool opt_v = false;
	const struct mbuf *m0 = NULL;
#endif
	int no = 0;
	char buf[512];

	while ((ch = *(modif++)) != '\0') {
		switch (ch) {
		case 'c':
			opt_c = true;
			break;
		case 'd':
			opt_d = true;
			break;
#if NETHER > 0
		case 'v':
			opt_v = true;
			m0 = m;
			break;
#endif
		default:
			break;
		}
	}

nextchain:
	(*pr)("MBUF(%d) %p\n", no, m);
	snprintb(buf, sizeof(buf), M_FLAGS_BITS, (u_int)m->m_flags);
	(*pr)("  data=%p, len=%d, type=%d, flags=%s\n",
	    m->m_data, m->m_len, m->m_type, buf);
	if (opt_d) {
		int i;
		unsigned char *p = m->m_data;

		(*pr)("  data:");

		for (i = 0; i < m->m_len; i++) {
			if (i % 16 == 0)
				(*pr)("\n");
			(*pr)(" %02x", p[i]);
		}

		(*pr)("\n");
	}
	(*pr)("  owner=%p, next=%p, nextpkt=%p\n", m->m_owner, m->m_next,
	    m->m_nextpkt);
	(*pr)("  leadingspace=%u, trailingspace=%u, readonly=%u\n",
	    (int)M_LEADINGSPACE(m), (int)M_TRAILINGSPACE(m),
	    (int)M_READONLY(m));
	if ((m->m_flags & M_PKTHDR) != 0) {
		snprintb(buf, sizeof(buf), M_CSUM_BITS, m->m_pkthdr.csum_flags);
		(*pr)("  pktlen=%d, rcvif=%p, csum_flags=%s, csum_data=0x%"
		    PRIx32 ", segsz=%u\n",
		    m->m_pkthdr.len, m_get_rcvif_NOMPSAFE(m),
		    buf, m->m_pkthdr.csum_data, m->m_pkthdr.segsz);
	}
	if ((m->m_flags & M_EXT)) {
		(*pr)("  ext_refcnt=%u, ext_buf=%p, ext_size=%zd, "
		    "ext_free=%p, ext_arg=%p\n",
		    m->m_ext.ext_refcnt,
		    m->m_ext.ext_buf, m->m_ext.ext_size,
		    m->m_ext.ext_free, m->m_ext.ext_arg);
	}
	if ((~m->m_flags & (M_EXT|M_EXT_PAGES)) == 0) {
		vaddr_t sva = (vaddr_t)m->m_ext.ext_buf;
		vaddr_t eva = sva + m->m_ext.ext_size;
		int n = (round_page(eva) - trunc_page(sva)) >> PAGE_SHIFT;
		int i;

		(*pr)("  pages:");
		for (i = 0; i < n; i ++) {
			(*pr)(" %p", m->m_ext.ext_pgs[i]);
		}
		(*pr)("\n");
	}

	if (opt_c) {
		m = m->m_next;
		if (m != NULL) {
			no++;
			goto nextchain;
		}
	}

#if NETHER > 0
	if (opt_v && m0)
		m_examine(m0, AF_ETHER, modif, pr);
#endif
}
#endif /* defined(DDB) */

#if defined(MBUFTRACE)
void
mowner_init_owner(struct mowner *mo, const char *name, const char *descr)
{
	memset(mo, 0, sizeof(*mo));
	strlcpy(mo->mo_name, name, sizeof(mo->mo_name));
	strlcpy(mo->mo_descr, descr, sizeof(mo->mo_descr));
}

void
mowner_attach(struct mowner *mo)
{

	KASSERT(mo->mo_counters == NULL);
	mo->mo_counters = percpu_alloc(sizeof(struct mowner_counter));

	/* XXX lock */
	LIST_INSERT_HEAD(&mowners, mo, mo_link);
}

void
mowner_detach(struct mowner *mo)
{

	KASSERT(mo->mo_counters != NULL);

	/* XXX lock */
	LIST_REMOVE(mo, mo_link);

	percpu_free(mo->mo_counters, sizeof(struct mowner_counter));
	mo->mo_counters = NULL;
}

void
mowner_init(struct mbuf *m, int type)
{
	struct mowner_counter *mc;
	struct mowner *mo;
	int s;

	m->m_owner = mo = &unknown_mowners[type];
	s = splvm();
	mc = percpu_getref(mo->mo_counters);
	mc->mc_counter[MOWNER_COUNTER_CLAIMS]++;
	percpu_putref(mo->mo_counters);
	splx(s);
}

void
mowner_ref(struct mbuf *m, int flags)
{
	struct mowner *mo = m->m_owner;
	struct mowner_counter *mc;
	int s;

	s = splvm();
	mc = percpu_getref(mo->mo_counters);
	if ((flags & M_EXT) != 0)
		mc->mc_counter[MOWNER_COUNTER_EXT_CLAIMS]++;
	if ((flags & M_EXT_CLUSTER) != 0)
		mc->mc_counter[MOWNER_COUNTER_CLUSTER_CLAIMS]++;
	percpu_putref(mo->mo_counters);
	splx(s);
}

void
mowner_revoke(struct mbuf *m, bool all, int flags)
{
	struct mowner *mo = m->m_owner;
	struct mowner_counter *mc;
	int s;

	s = splvm();
	mc = percpu_getref(mo->mo_counters);
	if ((flags & M_EXT) != 0)
		mc->mc_counter[MOWNER_COUNTER_EXT_RELEASES]++;
	if ((flags & M_EXT_CLUSTER) != 0)
		mc->mc_counter[MOWNER_COUNTER_CLUSTER_RELEASES]++;
	if (all)
		mc->mc_counter[MOWNER_COUNTER_RELEASES]++;
	percpu_putref(mo->mo_counters);
	splx(s);
	if (all)
		m->m_owner = &revoked_mowner;
}

static void
mowner_claim(struct mbuf *m, struct mowner *mo)
{
	struct mowner_counter *mc;
	int flags = m->m_flags;
	int s;

	s = splvm();
	mc = percpu_getref(mo->mo_counters);
	mc->mc_counter[MOWNER_COUNTER_CLAIMS]++;
	if ((flags & M_EXT) != 0)
		mc->mc_counter[MOWNER_COUNTER_EXT_CLAIMS]++;
	if ((flags & M_EXT_CLUSTER) != 0)
		mc->mc_counter[MOWNER_COUNTER_CLUSTER_CLAIMS]++;
	percpu_putref(mo->mo_counters);
	splx(s);
	m->m_owner = mo;
}

void
m_claim(struct mbuf *m, struct mowner *mo)
{

	if (m->m_owner == mo || mo == NULL)
		return;

	mowner_revoke(m, true, m->m_flags);
	mowner_claim(m, mo);
}

void
m_claimm(struct mbuf *m, struct mowner *mo)
{

	for (; m != NULL; m = m->m_next)
		m_claim(m, mo);
}
#endif /* defined(MBUFTRACE) */

#ifdef DIAGNOSTIC
/*
 * Verify that the mbuf chain is not malformed. Used only for diagnostic.
 * Panics on error.
 */
void
m_verify_packet(struct mbuf *m)
{
	struct mbuf *n = m;
	char *low, *high, *dat;
	int totlen = 0, len;

	if (__predict_false((m->m_flags & M_PKTHDR) == 0)) {
		panic("%s: mbuf doesn't have M_PKTHDR", __func__);
	}

	while (n != NULL) {
		if (__predict_false(n->m_type == MT_FREE)) {
			panic("%s: mbuf already freed (n = %p)", __func__, n);
		}
#if 0
		/*
		 * This ought to be a rule of the mbuf API. Unfortunately,
		 * many places don't respect that rule.
		 */
		if (__predict_false((n != m) && (n->m_flags & M_PKTHDR) != 0)) {
			panic("%s: M_PKTHDR set on secondary mbuf", __func__);
		}
#endif
		if (__predict_false(n->m_nextpkt != NULL)) {
			panic("%s: m_nextpkt not null (m_nextpkt = %p)",
			    __func__, n->m_nextpkt);
		}

		dat = n->m_data;
		len = n->m_len;
		if (__predict_false(len < 0)) {
			panic("%s: incorrect length (len = %d)", __func__, len);
		}

		low = M_BUFADDR(n);
		high = low + M_BUFSIZE(n);
		if (__predict_false((dat < low) || (dat + len > high))) {
			panic("%s: m_data not in packet"
			    "(dat = %p, len = %d, low = %p, high = %p)",
			    __func__, dat, len, low, high);
		}

		totlen += len;
		n = n->m_next;
	}

	if (__predict_false(totlen != m->m_pkthdr.len)) {
		panic("%s: inconsistent mbuf length (%d != %d)", __func__,
		    totlen, m->m_pkthdr.len);
	}
}
#endif

struct m_tag *
m_tag_get(int type, int len, int wait)
{
	struct m_tag *t;

	if (len < 0)
		return NULL;
	t = malloc(len + sizeof(struct m_tag), M_PACKET_TAGS, wait);
	if (t == NULL)
		return NULL;
	t->m_tag_id = type;
	t->m_tag_len = len;
	return t;
}

void
m_tag_free(struct m_tag *t)
{
	free(t, M_PACKET_TAGS);
}

void
m_tag_prepend(struct mbuf *m, struct m_tag *t)
{
	KASSERT((m->m_flags & M_PKTHDR) != 0);
	SLIST_INSERT_HEAD(&m->m_pkthdr.tags, t, m_tag_link);
}

void
m_tag_unlink(struct mbuf *m, struct m_tag *t)
{
	KASSERT((m->m_flags & M_PKTHDR) != 0);
	SLIST_REMOVE(&m->m_pkthdr.tags, t, m_tag, m_tag_link);
}

void
m_tag_delete(struct mbuf *m, struct m_tag *t)
{
	m_tag_unlink(m, t);
	m_tag_free(t);
}

void
m_tag_delete_chain(struct mbuf *m)
{
	struct m_tag *p, *q;

	KASSERT((m->m_flags & M_PKTHDR) != 0);

	p = SLIST_FIRST(&m->m_pkthdr.tags);
	if (p == NULL)
		return;
	while ((q = SLIST_NEXT(p, m_tag_link)) != NULL)
		m_tag_delete(m, q);
	m_tag_delete(m, p);
}

struct m_tag *
m_tag_find(const struct mbuf *m, int type)
{
	struct m_tag *p;

	KASSERT((m->m_flags & M_PKTHDR) != 0);

	p = SLIST_FIRST(&m->m_pkthdr.tags);
	while (p != NULL) {
		if (p->m_tag_id == type)
			return p;
		p = SLIST_NEXT(p, m_tag_link);
	}
	return NULL;
}

struct m_tag *
m_tag_copy(struct m_tag *t)
{
	struct m_tag *p;

	p = m_tag_get(t->m_tag_id, t->m_tag_len, M_NOWAIT);
	if (p == NULL)
		return NULL;
	memcpy(p + 1, t + 1, t->m_tag_len);
	return p;
}

/*
 * Copy two tag chains. The destination mbuf (to) loses any attached
 * tags even if the operation fails. This should not be a problem, as
 * m_tag_copy_chain() is typically called with a newly-allocated
 * destination mbuf.
 */
int
m_tag_copy_chain(struct mbuf *to, struct mbuf *from)
{
	struct m_tag *p, *t, *tprev = NULL;

	KASSERT((from->m_flags & M_PKTHDR) != 0);

	m_tag_delete_chain(to);
	SLIST_FOREACH(p, &from->m_pkthdr.tags, m_tag_link) {
		t = m_tag_copy(p);
		if (t == NULL) {
			m_tag_delete_chain(to);
			return 0;
		}
		if (tprev == NULL)
			SLIST_INSERT_HEAD(&to->m_pkthdr.tags, t, m_tag_link);
		else
			SLIST_INSERT_AFTER(tprev, t, m_tag_link);
		tprev = t;
	}
	return 1;
}